itojun@iijlab.net writes:

> >> And if you do: 
> >> ifconfig lo0 192.168.127.26 netmask 255.255.255.255 alias
> >Same thing. When I set with ifconfig, it works. When I set with my
> >program, using SIOCAIFADDR, it doesn't work, even if the output from
> >netstat -rn and ifconfig -A lo0 is exactly the same.
> 
> 	if you could post your program somewhere someone could debug it.

Ok. Here's my small test program, which doesn't work. 

Running: 
  ./iftest lo0 192.168.127.26 255.255.255.0

should, AFAIK, be the same as: 
  ifconfig lo0 192.168.127.26 netmask 255.255.255.0 

--- iftest.c ---
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>

int main(int argc, char *argv[])
{
  struct ifaliasreq ifra;
  struct sockaddr_in ip;
  int s;

  if(argc < 4) {
    printf("Usage: %s <if> <ip> <netmask>\n", argv[0]);
    exit(1);
  }

  s = socket(PF_INET, SOCK_DGRAM, 0);
  if(s < 0) {
    perror("socket");
    exit(1);
  }

  memset(&ifra, 0, sizeof(struct ifaliasreq));
  strncpy(ifra.ifra_name, argv[1], IFNAMSIZ);
  ip.sin_len = sizeof(struct sockaddr_in);
  ip.sin_family = AF_INET;
  inet_aton(argv[2], &ip.sin_addr);
  memcpy(&ifra.ifra_addr, &ip, sizeof(struct sockaddr_in));
  inet_aton(argv[3], &ip.sin_addr);
  memcpy(&ifra.ifra_mask, &ip, sizeof(struct sockaddr_in));
  if(ioctl(s, SIOCAIFADDR, &ifra) < 0)
    perror("ioctl");

  close(s);

  return 0;
}
--- EOF ---



Greetings,

Tomas